Power amplifiers, being one of the last stages of the transmitter branch of a wireless communication system, are one of the key components that heavily affects the overall performance. Nowadays communication systems are required to be compact and affordable. For their cooling system to be simple and small the power amplifiers should be efficient. The evolution of wireless communications moves toward higher data rates which need wider frequency bands and higher complexity modulation schemes. These solutions lead to a high peak-to-average power ratio, therefore the ability of a power amplifier to maintain its performance in terms of efficiency and linearity for lower power levels has become crucial.